Organic electroluminescent materials and devices

ABSTRACT

According to one embodiment, a compound comprising a ligand L A  of Formula I 
     
       
         
         
             
             
         
       
     
     is described. In the structure of Formula I, A 1  through A 8  are independently carbon or nitrogen, with at least one being nitrogen; X 1  is selected from the group consisting of O, S, and Se; X 2  and X 3  are independently selected from the group consisting of C, N, O, P, and S; ring A is a 5- or 6-membered heterocyclic ring bonded to ring B through a X 2 —C bond and bonded to M through a metal-carbene bond; any adjacent substitutions in R 1  and R 2  are optionally linked together to form a ring; the ligand L A  is coordinated to a metal M; and the ligand L A  is optionally linked with other ligands to comprise up to a hexadentate ligand. Formulations and devices, such as an OLEDs, that include the compound comprising ligand L A  of formula I are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/907,450, filed Nov. 22, 2013, and U.S. Provisional PatentApplication Ser. No. 61/904,530, filed Nov. 15, 2013, the entirecontents of which are incorporated herein by reference.

PARTIES TO A JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to compounds for use as emitters anddevices, such as organic light emitting diodes, including the same.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule istris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the followingstructure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

According to one embodiment, a compound comprising a ligand L_(A) ofFormula I:

is provided.

In the structure of Formula I:

-   -   each A¹, A², A³, A⁴, A⁵, A⁶, A⁷, and A⁸ is independently carbon        or nitrogen;    -   at least one of A¹, A², A³, A⁴, A⁵, A⁶, A⁷, and A⁸ is nitrogen;    -   X¹ is selected from the group consisting of O, S, and Se;    -   X² and X³ each independently comprise an atom selected from the        group consisting of C, N, O, P, and S;    -   ring A is bonded to ring B through a X²—C bond;    -   ring A is a 5- or 6-member heterocyclic ring;    -   R¹ and R² each independently represent mono, di, tri, or        tetra-substitution, or no substitution;    -   any adjacent substitutions in R¹ and R² are optionally linked        together to form a ring;    -   R¹ and R² are each independently selected from the group        consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,        heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,        cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl,        carbonyl, carboxylic acids, ester, nitrile, isonitrile,        sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations        thereof;    -   the ligand L_(A) is coordinated to a metal M;    -   M is coordinated to ring A through a metal-carbene bond; and    -   the ligand L_(A) is optionally linked with other ligands to        comprise a tridentate, tetradentate, pentadentate or hexadentate        ligand.

According to another embodiment, a first device comprising a firstorganic light emitting device is also provided. The first organic lightemitting device can include an anode, a cathode, and an organic layer,disposed between the anode and the cathode. The organic layer caninclude a compound comprising a ligand L_(A) of Formula I. The firstdevice can be one or more of a a consumer product, an electroniccomponent module, an organic light-emitting device, and a lightingpanel.

Formulations containing a compound comprising a ligand L_(A) of FormulaI are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows a ligand L_(A) of Formula I as disclosed herein.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No, 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink-jet and OVJD. Othermethods may also be used. The materials to be deposited may be modifiedto make them compatible with a particular deposition method. Forexample, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US20071023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention canbe incorporated into a wide variety of electronic component modules (orunits) that can be incorporated into a variety of electronic products orintermediate components. Examples of such electronic products orintermediate components include display screens, lighting devices suchas discrete light source devices or lighting panels, etc. that can beutilized by the end-user product manufacturers. Such electroniccomponent modules can optionally include the driving electronics and/orpower source(s). Devices fabricated in accordance with embodiments ofthe invention can be incorporated into a wide variety of consumerproducts that have one or more of the electronic component modules (orunits) incorporated therein. Such consumer products would include anykind of products that include one or more light source(s) and/or one ormore of some type of visual displays. Some examples of such consumerproducts include flat panel displays, computer monitors, medicalmonitors, televisions, billboards, lights for interior or exteriorillumination and/or signaling, heads-up displays, fully or partiallytransparent displays, flexible displays, laser printers, telephones,cell phones, tablets, phablets, personal digital assistants (PDAs),laptop computers, digital cameras, camcorders, viewfinders,micro-displays, 3-D displays, vehicles, a large area wall, theater orstadium screen, or a sign. Various control mechanisms may be used tocontrol devices fabricated in accordance with the present invention,including passive matrix and active matrix. Many of the devices areintended for use in a temperature range comfortable to humans, such as18 degrees C. to 30 degrees C., and more preferably at room temperature(20-25 degrees C.), but could be used outside this temperature range,for example, from −40 degree C. to +80 degree C.

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The term “halo,” “halogen,” or “halide” as used herein includesfluorine, chlorine, bromine, and iodine.

The term “alkyl” as used herein contemplates both straight and branchedchain alkyl radicals. Preferred alkyl groups are those containing fromone to fifteen carbon atoms and includes methyl, ethyl, propyl,isopropyl, isobutyl, tert-butyl, and the like. Additionally, the alkylgroup may be optionally substituted.

The term “cycloalkyl” as used herein contemplates cyclic alkyl radicals.Preferred cycloalkyl groups are those containing 3 to 7 carbon atoms andincludes cyclopropyl, cyclopentyl, cyclohexyl, and the like.Additionally, the cycloalkyl group may be optionally substituted.

The term “alkenyl” as used herein contemplates both straight andbranched chain alkene radicals. Preferred alkenyl groups are thosecontaining two to fifteen carbon atoms. Additionally, the alkenyl groupmay be optionally substituted.

The term “alkynyl” as used herein contemplates both straight andbranched chain alkyne radicals. Preferred alkynyl groups are thosecontaining two to fifteen carbon atoms. Additionally, the alkynyl groupmay be optionally substituted.

The terms “aralkyl” or “arylalkyl” as used herein are usedinterchangeably and contemplate an alkyl group that has as a substituentan aromatic group. Additionally, the aralkyl group may be optionallysubstituted.

The term “heterocyclic group” as used herein contemplates aromatic andnon-aromatic cyclic radicals. Hetero-aromatic cyclic radicals also meansheteroaryl. Preferred hetero-non-aromatic cyclic groups are thosecontaining 3 or 7 ring atoms which includes at least one hetero atom,and includes cyclic amines such as morpholino, piperdino, pyrrolidino,and the like, and cyclic ethers, such as tetrahydrofuran,tetrahydropyran, and the like. Additionally, the heterocyclic group maybe optionally substituted.

The term “aryl” or “aromatic group” as used herein contemplatessingle-ring groups and polycyclic ring systems. The polycyclic rings mayhave two or more rings in which two carbons are common to two adjoiningrings (the rings are “fused”) wherein at least one of the rings isaromatic, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl,heterocycles, and/or heteroaryls. Additionally, the aryl group may beoptionally substituted.

The term “heteroaryl” as used herein contemplates single-ringhetero-aromatic groups that may include from one to three heteroatoms,for example, pyrrole, furan, thiophene, imidazole, oxazole, thiazole,triazole, pyrazole, pyridine, pyrazine and pyrimidine, and the like. Theterm heteroaryl also includes polycyclic hetero-aromatic systems havingtwo or more rings in which two atoms are common to two adjoining rings(the rings are “fused”) wherein at least one of the rings is aheteroaryl, e.g., the other rings can be cycloalkyls, cycloalkenyls,aryl, heterocycles, and/or heteroaryls. Additionally, the heteroarylgroup may be optionally substituted.

The alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, heterocyclic group,aryl, and heteroaryl may be optionally substituted with one or moresubstituents selected from the group consisting of hydrogen, deuterium,halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether,ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof.

As used herein, “substituted” indicates that a substituent other than His bonded to the relevant position, such as carbon. Thus, for example,where R¹ is mono-substituted, then one R¹ must be other than H.Similarly, where R¹ is di-substituted, then two of R¹ must be other thanH. Similarly, where R¹ is unsubstituted, R¹ is hydrogen for allavailable positions.

The “aza” designation in the fragments described herein, i.e.aza-dibenzofuran, aza-dibenzothiophene, etc. means that one or more ofthe C—H groups in the respective fragment can be replaced by a nitrogenatom, for example, and without any limitation, azatriphenyleneencompasses both dibenzo[f,h]quinoxaline and dibenzo[f,h]quinoline. Oneof ordinary skill in the art can readily envision other nitrogen analogsof the aza-derivatives described above, and all such analogs areintended to be encompassed by the terms as set forth herein.

It is to be understood that when a molecular fragment is described asbeing a substituent or otherwise attached to another moiety, its namemay be written as if it were a fragment (e.g. phenyl, phenylene,naphthyl, dibenzofuryl) or as if it were the whole molecule (e.g.benzene, naphthalene, dibenzofuran). As used herein, these differentways of designating a substituent or attached fragment are considered tobe equivalent.

The compounds described herein are metal complexes containing anazadibenzofuranyl imidazole carbene ligand. The introduction of theazadibenzofuran moiety can lower the LUMO of the complex compared todibenzofuran containing complexes, resulting in better device stability.In addition, the rigidity of the ligand containing the azadibenzofuranmoiety makes the emission spectrum narrower, which is desirable for moresaturated colors.

According to one embodiment, a compound comprising a ligand L_(A) ofFormula I:

is disclosed.

In the structure of Formula I:

-   -   each A¹, A², A³, A⁴, A⁵, A⁶, A⁷, and A⁸ is independently carbon        or nitrogen;    -   at least one of A¹, A², A³, A⁴, A⁵, A⁶, A⁷, and A⁸ is nitrogen;    -   X¹ is selected from the group consisting of O; S, and Se;    -   X² and X³ each independently comprise an atom selected from the        group consisting of C, N, O, P, and S;    -   ring A is bonded to ring B through a X²—C bond;    -   ring A is a 5- or 6-member heterocyclic ring;    -   R¹ and R² each independently represent mono, di, tri, or        tetra-substitution, or no substitution;    -   any adjacent substitutions in R¹ and R² optionally linked        together to form a ring;    -   R¹ and R² are each independently selected from the group        consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,        heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,        cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl,        carbonyl, carboxylic acids, ester, nitrile, isonitrile,        sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations        thereof;    -   the ligand L_(A) is coordinated to a metal M;    -   M is coordinated to ring A through a metal-carbene bond; and    -   the ligand L_(A) is optionally linked with other ligands to        comprise a tridentate, tetradentate, pentadentate or hexadentate        ligand.

In some embodiments, the compound has the formulaM(L_(A))_(m)(L_(B))_(n) of the structure:

In the structure of Formula II:

-   -   L_(B) is a different ligand from L_(A);    -   m is an integer from 1 to the maximum number of ligands that may        be coordinated to the metal M; and    -   m+n is the the maximum number of ligands that may be coordinated        to the metal M.

In some embodiments, M is selected from the group consisting of Ir, Rh,Re, Ru, Os, Pt, Au, and Cu. In some embodiments, M is Ir.

In some embodiments, X¹ is O. In some embodiments, M is coordinated toring B through a M-C bond.

In some embodiments, only one of A¹, A², A³, A⁴, A⁵, A⁶, A⁷, and A⁸ isnitrogen. In some embodiments, each one of A¹, A², A³, and A⁴ is carbon.In some embodiments, each one of A¹, A², A³, and A⁴ is carbon, andexactly one of A⁵, A⁶, A⁷, and A⁸ is nitrogen. In some embodiments, onlytwo of A¹, A², A³, A⁴, A⁵, A⁶, A⁷, and A⁸ are nitrogen. In someembodiments, each one of A¹, A², A³, and A⁴ is carbon, and exactly twoof A⁵, A.⁶, A⁷, and A⁸ are nitrogen.

In some embodiments, R² forms a phenyl or pyridyl ring fused to ring A.In some embodiments, R² forms a phenyl or pyridyl ring fused to ring A,and the phenyl or pyridyl ring (ring A) is further substituted. In someembodiments, ring A is selected from the group consisting of:

-   -   where the wave line indicates the bond to ring B; and    -   where R³ is selected from the group consisting of hydrogen,        deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,        alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,        heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,        carboxylic acids, ester, nitrile, isonitrile, sulfanyl,        sulfinyl, sulfonyl, phosphino, and combinations thereof.

In some embodiments, the ligand L_(A) is

where R³ is selected from the group consisting of hydrogen, deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof.

In some embodiments, the compound has the formulaIr(L_(A))_(m)(L_(B))_(n), having the structure

where m+n=3, and R³ is selected from the group consisting of hydrogen,deuterium, halide, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrite,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof.

In some embodiments, the compound is selected from the group consistingof

In these structures:

-   -   R⁴ represents mono, di-substitution, or no substitution;    -   R⁶, R⁸ and R⁹ each independently represent mono, di, tri, or        tetra-substitution, or no substitution;    -   Y¹, Y², Y³, Y⁴, Y⁵, Y⁶, Y⁷, and Y⁸ comprise carbon or nitrogen;    -   R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ are each independently selected from        the group consisting of hydrogen, deuterium, halide, alkyl,        cycloalkyl, heteroalkyl, arylalkyl, aryloxy, amino, alkenyl,        cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl,        carbonyl, carboxylic acids, ester, nitrile, isonitrile,        sulfanyl, sulfonyl, phosphino, and combinations thereof; and    -   any adjacent substitutions in R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸ and        R⁹ are optionally linked together to form a ring.

In some embodiments, the compound is selected from the group consistingof

In these structures:

-   -   R⁴ represents mono, di-substitution, or no substitution;    -   R⁶, R⁸ and R⁹ each independently represent mono, di, tri, or        tetra-substitution, or no substitution;    -   Y¹, Y², Y³, Y⁴, Y⁵, Y⁶, Y⁷, and Y⁸ comprise carbon or nitrogen;    -   R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ are each independently selected from        the group consisting of hydrogen, deuterium, halide, alkyl,        cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino,        silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,        heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,        isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and        combinations thereof; and    -   any adjacent substitutions in R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸ and        R⁹ are optionally linked together to form a ring.

In some embodiments, m is 1. In some embodiments, R¹ is selected fromthe group consisting of hydrogen, deuterium, alkyl, cycloalkyl, andcombinations thereof. In some embodiments, R¹ is selected from the groupconsisting of methyl, ethyl, isopropuyl, isobutyl, cyclopentyl andpartially or fully deuterated variations thereof.

In some embodiments, R² is selected from the group consisting ofhydrogen, a phenyl ring fused to ring A, and a pyridyl ring fused toring A. In some embodiments, R³ is alkyl or cycloalkyl. In someembodiments, R³ is aryl or substituted aryl. In some more specificembodiments, R³ is selected from the group consisting of: methyl, ethyl,propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, pentyl,1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl,1,2-dimethylpropyl, 2,2-dimethylpropyl, cyclopentyl, and cyclohexyl,wherein each group is optionally partially or fully deuterated.

In some embodiments, R⁵ is selected from the group consisting of alkyl,cycloalkyl, aryl and substituted aryl. In some embodiments, R⁷ is a2,6-disubstituted aryl. In some embodiments, R⁷ is a 2,6-disubstitutedphenyl, substituted with an alkyl selected from the group consisting ofmethyl, ethyl, isopropyl, isobutyl, and partially or fully deuteratedvariations thereof. In some embodiments, R⁷ comprises at least onechemical group selected from the group consisting of carbazole,dibenzothiophene, dibenzofuran, and fluorine.

In some embodiments, Y⁵, Y⁶, Y⁷, and Y⁸ comprise carbon, only one of Y¹,Y², Y³, Y⁴ is nitrogen. In some embodiments, Y² is nitrogen.

In some embodiments, R⁸ is selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, and combinationsthereof. In some embodiments, R⁸ is selected from the group consistingof methyl, ethyl, isopropyl, isobutyl, and partially or fully deuteratedvariations thereof. In some embodiments, adjacent R⁸ substituents arejoined together with Ring C to form dibenzofuran, azadibenzofuran,dibenzothiophene, or azadibenzothiophene.

In some embodiments, R⁹ is selected from the group consisting ofhydrogen, deuterium, alkyl, cycloalkyl, and combinations thereof. Insome embodiments, R⁹ is selected from the group consisting of methyl,ethyl, isopropyl, isobutyl, deuterated variations thereof, phenyl, alkylsubstituted phenyl, pyridyl, alkyl substituted pyridyl, fused phenyl,and alkyl substituted fused phenyl.

In some embodiments, the ligand L_(A) is:

-   -   R¹⁰ is selected from the group consisting of of hydrogen,        deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,        alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,        heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,        carboxylic acids, ester, nitrile, isonitrile, sulfanyl,        sulfinyl, sulfonyl, phosphino, and combinations thereof.

In some embodiments, ligand L_(A) is

In some embodiments, R¹⁰) is selected from the group consisting ofhydrogen, deuterium, alkyl, and combinations thereof. In someembodiments, R¹⁰ is alkyl. In some embodiments, R¹⁰ is cycloalkyl. Insome embodiments, R¹⁰ is selected from the group consisting of methyl,ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl,pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl,1,2-dimethylpropyl, 2,2-dimethylpropyl, cyclopentyl, cyclohexyl,partially or fully deuterated variants thereof, and combinationsthereof.

In some embodiments, L_(A) is selected from the group consisting of:

In some embodiments, L_(B) is selected from the group consisting of:

In some embodiments, L_(A1) to L_(A80) have the definitions herein,L_(B1) to L_(B76) have the definitions herein, and the compound isselected from the group consisting of Compound 1 to Compound 6080, whereeach Compound x has the formula Ir(L_(Ak))(L_(Bj))₂, wherein x=80j+k−80,k is an integer from 1 to 80, and j is an integer from 1 to 76.

In some embodiments, the compound can be an emissive dopant. In someembodiments, the compound can produce emissions via phosphorescence,fluorescence, thermally activated delayed fluorescence, i.e., TADF (alsoreferred to as E-type delayed fluorescence), triplet-tripletannihilation, or combinations of these processes.

According to another aspect of the present disclosure, a first device isalso provided. The first device includes a first organic light emittingdevice, that includes an anode, a cathode, and an organic layer disposedbetween the anode and the cathode. The organic layer can includecompound comprising a ligand L_(A) of Formula I and its variants asdescribed herein. In some embodiments, the organic layer includes a hostand a phosphorescent dopant.

The first device can be one or more of a a consumer product, anelectronic component module, an organic light-emitting device, and alighting panel. The organic layer can be an emissive layer and thecompound can be an emissive dopant in some embodiments, while thecompound can be a non-emissive dopant in other embodiments.

The organic layer can also include a host. In some embodiments, the hostcan include a metal complex. The host can be a triphenylene containingbenzo-fused thiophene or benzo-fused furan. Any substituent in the hostcan be an unfused substituent independently selected from the groupconsisting of C_(n)H_(2n|1), OC_(n)H_(2n|1), OAr₁, N(C_(n)H_(2n|1))₂,N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n|1), C≡C—C_(n)H_(2n+1), Ar₁, Ar₁—Ar₂, andC_(n)H_(2n)—Ar₁, or no substitution. In the preceding substituents n canrange from 1 to 10; and Ar₁ and Ar₂ can be independently selected fromthe group consisting of benzene, biphenyl, naphthalene, triphenylene,carbazole, and heteroaromatic analogs thereof.

The host can be a compound comprising at least one chemical groupselected from the group consisting of triphenylene, carbazole,dibenzothiophene, dibenzofuran, dibenzoselenophene, azatriphenylene,azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, andaza-dibenzoselenophene. The host can include a metal complex. The hostcan be a specific compound selected from the group consisting of:

and combinations thereof.

In yet another aspect of the present disclosure, a formulation thatcomprises a compound comprising a ligand L_(A) of Formula I, and itsvariations described herein, is described. The formulation can includeone or more components selected from the group consisting of a solvent,a host, a hole injection material, hole transport material, and anelectron transport layer material, disclosed herein.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in the presentinvention is not particularly limited, and any compound may be used aslong as the compound is typically used as a hole injecting/transportingmaterial. Examples of the material include, but not limit to: aphthalocyanine or porphyrin derivative; an aromatic amine derivative; anindolocarbazole derivative; a polymer containing fluorohydrocarbon; apolymer with conductivity dopants; a conducting polymer, such asPEDOT/PSS; a self-assembly monomer derived from compounds such asphosphoric acid and silane derivatives; a metal oxide derivative, suchas MoO_(x); a p-type semiconducting organic compound, such as1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and across-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, butnot limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting of aromatichydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl,triphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, and azulene; the group consistingof aromatic heterocyclic compounds such as dibenzothiophene,dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran,benzothiophene, benzoselenophene, carbazole, indolocarbazole,pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole,oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole,pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine,oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine,benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline,cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine,pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine,benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and the group consisting of 2 to 10 cyclic structural units which aregroups of the same type or different types selected from the aromatichydrocarbon cyclic group and the aromatic heterocyclic group and arebonded to each other directly or via at least one of oxygen atom,nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom,chain structural unit and the aliphatic cyclic group. Wherein each Ar isfurther substituted by a substituent selected from the group consistingof hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the groupconsisting of:

wherein k is an integer from 1 to 20; X¹⁰¹ to X¹⁰⁸ is C (including CH)or N; Z¹⁰¹ is NAr¹, O, or S; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but not limit tothe following general formula:

wherein Met is a metal, which can have an atomic weight greater than 40;(Y¹⁰¹-Y¹⁰²) is a bidentate ligand, Y¹⁰¹ and Y¹⁰² are independentlyselected from C, N, O, P, and S; L¹⁰¹ is an ancillary ligand; k′ is aninteger value from 1 to the maximum number of ligands that may beattached to the metal; and k′+k″ is the maximum number of ligands thatmay be attached to the metal.

In one aspect, (Y¹⁰¹-Y¹⁰²) is a 2-phenylpyridine derivative. In anotheraspect, (Y¹⁰¹-Y¹⁰²) is a carbene ligand. In another aspect, Met isselected from Ir, Pt, Os, and Zn. In a further aspect, the metal complexhas a smallest oxidation potential in solution vs. Fc⁻/Fc couple lessthan about 0.6 V.

Host:

The light emitting layer of the organic EL device of the presentinvention preferably contains at least a metal complex as light emittingmaterial, and may contain a host material using the metal complex as adopant material. Examples of the host material are not particularlylimited, and any metal complexes or organic compounds may be used aslong as the triplet energy of the host is larger than that of thedopant. While the Table below categorizes host materials as preferredfor devices that emit various colors, any host material may be used withany dopant so long as the triplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have thefollowing general formula:

wherein Met is a metal; (Y¹⁰³-Y¹⁰⁴) is a bidentate ligand, Y¹⁰³ and Y¹⁰⁴are independently selected from C, N, O, P, and S; L¹⁰¹ is an anotherligand; k′ is an integer value from 1 to the maximum number of ligandsthat may be attached to the metal; and k′+k″ is the maximum number ofligands that may be attached to the metal.

In one aspect, the metal complexes are:

wherein (O—N) is a bidentate ligand, having metal coordinated to atoms Oand N.

In another aspect, Met is selected from Ir and Pt. In a further aspect,(Y¹⁰³-Y¹⁰⁴) is a carbene ligand.

Examples of organic compounds used as host are selected from the groupconsisting of aromatic hydrocarbon cyclic compounds such as benzene,biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene,phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene; thegroup consisting of aromatic heterocyclic compounds such asdibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene,benzofuran, benzothiophene, benzoselenophene, carbazole,indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole,triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole,thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine,oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole,indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline,isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine,phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine,phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and the group consisting of 2 to 10 cyclic structural units which aregroups of the same type or different types selected from the aromatichydrocarbon cyclic group and the aromatic heterocyclic group and arebonded to each other directly or via at least one of oxygen atom,nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom,chain structural unit and the aliphatic cyclic group. Wherein each groupis further substituted by a substituent selected from the groupconsisting of hydrogen, deuterium, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrite, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof.

In one aspect, the host compound contains at least one of the followinggroups in the molecule:

wherein R¹⁰¹ to R¹⁰⁷ is independently selected from the group consistingof hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof, when it is aryl or heteroaryl, ithas the similar definition as Ar's mentioned above. k is an integer from0 to 20 or 1 to 20; k′″ is an integer from 0 to 20. X¹⁰¹ to X¹⁰⁸ isselected from C (including CH) or N. Z¹⁰¹ and Z¹⁰² is selected fromNR¹⁰¹, O, or S.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies as compared to a similar device lacking a blocking layer.Also, a blocking layer may be used to confine emission to a desiredregion of an OLED.

In one aspect, compound used in HBL contains the same molecule or thesame functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of thefollowing groups in the molecule:

wherein k is an integer from 1 to 20; L¹⁰¹ is an another ligand, k′ isan integer from 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable oftransporting electrons. Electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, compound used in ETL contains at least one of thefollowing groups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen,deuterium, halide, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof, when it is aryl or heteroaryl, it has the similar definition asAr's mentioned above. Ar¹ to Ar³ has the similar definition as Ar'smentioned above. k is an integer from 1 to 20. X¹⁰¹ to X¹⁰⁸ is selectedfrom C (including CH) or N.

In another aspect, the metal complexes used in ETL contains, but notlimit to the following general formula:

wherein (O—N) or (N—N) is a bidentate ligand, having metal coordinatedto atoms O, N or N, N; L¹⁰¹ is another ligand; k′ is an integer valuefrom 1 to the maximum number of ligands that may be attached to themetal.

In any above-mentioned compounds used in each layer of the OLED device,the hydrogen atoms can be partially or fully deuterated. Thus, anyspecifically substituent, such as, without limitation, methyl, phenyl,pyridyl, etc. encompasses undeuterated, partially deuterated, and fullydeuterated versions thereof. Similarly, classes of substituents such as,without limitation, alkyl, aryl, cycloalkyl, heteroaryl, etc. alsoencompass undeuterated, partially deuterated, and fully deuteratedversions thereof.

In addition to and/or in combination with the materials disclosedherein, many hole injection materials, hole transporting materials, hostmaterials, dopant materials, exiton/hole blocking layer materials,electron transporting and electron injecting materials may be used in anOLED. Non-limiting examples of the materials that may be used in an OLEDin combination with materials disclosed herein are listed in Table Abelow. Table A lists non-limiting classes of materials, non-limitingexamples of compounds for each class, and references that disclose thematerials.

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EXPERIMENTAL Synthesis of (L_(A1))₃Ir Synthesis of3-methyl-1-2-methylbenzofuro[2,3-b]pyridin-8-yl)-1H-imidazol-3-iumiodide

Iodomethane (5.6 mL, 90 mmol) was added to8-(1H-imidazol-1-yl)-2-methylbenzofuro[2,3-b]pyridine (4.5 g, 18.1 mmol)in 50 mL of acetonitrile. The reaction mixture was then brought toreflux for 10 minutes before being stirred at room temperature for twodays. The reaction mixture was filtered and washed with ethyl acetateand dichloromethane (DCM) to yield 5.3 g (75%) of3-methyl-1-(2-methylbenzofuro[2,3-b]pyridin-8-yl)-1H-imidazol-3-iumiodide.

Synthesis of (L_(A1))₃Ir

To 3-methyl-1-(2-methylbenzofuro[2,3-b]pyridin-8-yl)-1H-imidazol-3-iumiodide (1 g, 2.6 mmol) was added 50 mL dimethylformamide (DMF) followedby silver(I) oxide (0.59 g, 2.6 mmol) and [(COD)IrCl]₂ (0.21 g, 0.32mmol). The reaction mixture was heated to 145° C. for 20 h and theresulting mixture was filtered through a plug of celite and washed withdichloromethane (DCM). The solvent was evaporated and the productchromatographed on basic silica with 0-10% ethyl acetate in DCM to yield0.3 g (97%) of (L_(A1))₃Ir.

Synthesis of Compound 963 (L_(B13))₂Ir(L_(A3))) Synthesis of3-isopropyl-1-(2-methylbenzofuro[2,3-b]pyridin-8-yl)-1H-imidazol-3-iumiodide

2-Iodopropane (2.1 mL, 20.9 mmol) was added to8-(1H-imidazol-1-yl)-2-methylbenzofuro[2,3-b]pyridine (2.6 g, 10.4 mmol)in 50 mL of acetonitrile and the reaction was heated to 80° C. for 2days. The solvent was evaporated and the residue washed withacetonitrile to yield 3.5 g (80%) of3-isopropyl-1-(2-methylbenzofuro[2,3-b]pyridin-8-yl)-1H-imidazol-3-iumiodide.

Synthesis of Compound 963

Silver(I) oxide (1.0 g, 4.3 mmol) was added to3-isopropyl-1-(2-methylbenzofuro[2,3-b]pyridin-8-yl)-1H-imidazol-3-iumiodide (3.0 g, 7.2 mmol) in 50 ml of acetonitrile. The reaction wasstirred at room temperature under nitrogen overnight and the solventevaporated. The iridium dimer (3.5 g, 1.8 mmol) and 50 mL, oftetrahydrofuran (THF) were added and the reaction mixture, which wasthen brought to reflux overnight. After cooling to room temperature, thereaction mixture was filtered through a plug of celite and washed withDCM. After evaporation of the solvent, the crude product waschromatographed on basic silica with 10-20% DCM in heptane to yield 3.8g (86%) of the meridional isomer of Compound 963. This material wasdissolved in DMSO and thoroughly degassed before being irradiated withUV light for 20 h. After removing the solvent, the residue waschromatographed on basic silica gel with 15-25% DCM in heptane. Afterremoval of the solvent, the material was washed with methanol to yield1.0 g (26%) of Compound 963 (facial isomer).

The properties of Compound 963 were compared against ComparativeCompound 1. A 5% doped PMMA film of Comparative Compound 1 exhibited a56% PLQY, whereas a 5% doped PMMA film of Compound 963 exhibited a PLQYof 86%, which is much higher than that of the comparative compound. Itis adantageous to have higher PLQY as an emitter in the OLED device.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

1. A compound comprising a ligand L_(A) of Formula I:

wherein each A¹, A², A³, A⁴, A⁵, A⁶, A⁷, and A⁸ is independently carbonor nitrogen; wherein at least one of A¹, A², A³, A⁴, A⁵, A⁶, A⁷, and A⁸is nitrogen; wherein X¹ is selected from the group consisting of O, S,and Se; wherein X² and X³ each independently comprise an atom selectedfrom the group consisting of C, N, O, P, and S; wherein ring A is bondedto ring B through a X²—C bond; wherein ring A is a 5- or 6-memberheterocyclic ring; wherein R¹ and R² each independently represent mono,di, tri, or tetra-substitution, or no substitution; wherein any adjacentsubstitutions in R¹ and R² are optionally linked together to form aring; wherein R¹ and R² are each independently selected from the groupconsisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof; wherein the ligand L_(A)is coordinated to a metal M; wherein M is coordinated to ring A througha metal-carbene bond; and wherein the ligand L_(A) is optionally linkedwith other ligands to comprise a tridentate, tetradentate, pentadentateor hexadentate ligand.
 2. The compound of claim 1, wherein the compoundhas the formula M(L_(A))_(m)(L_(B))_(n), having the structure:

wherein L_(B) is a different ligand from L_(A); wherein m is an integerfrom 1 to the maximum number of ligands that may be coordinated to themetal M; and m+n is the the maximum number of ligands that may becoordinated to the metal M.
 3. The compound of claim 1, wherein M isselected from the group consisting of Ir, Rh, Re, Ru, Os, Pt, Au, andCu.
 4. The compound of claim 1, wherein M is Ir.
 5. The compound ofclaim 1, wherein X¹ is O.
 6. The compound of claim 1, wherein M iscoordinated to ring B through a M-C bond.
 7. The compound of claim 1,wherein one of A¹, A², A³, A⁴, A⁵, A⁶, A⁷, and A⁸ is nitrogen.
 8. Thecompound of claim 1, wherein each one of A¹, A², A³, and A⁴ is carbon.9. The compound of claim 1, wherein each one of A¹, A², A³, and A⁴ iscarbon, and exactly one of A⁵, A⁶, A⁷, and A⁸ is nitrogen.
 10. Thecompound of claim 1, wherein R² forms a phenyl or pyridyl ring fused toring A; and wherein the phenyl or pyridyl ring may be furthersubstituted.
 11. The compound of claim 1, wherein ring A is selectedfrom the group consisting of:

wherein the wave line indicates the bond to ring B; wherein R³ isselected from the group consisting of hydrogen, deuterium, halide,alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino,silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl,acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfonyl,sulfinyl, sulfonyl, phosphino, and combinations thereof.
 12. Thecompound of claim 1, wherein the ligand L_(A) is:

wherein R³ is selected from the group consisting of hydrogen, deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof.
 13. The compound of claim 2, wherein the compound has theformula Ir(L_(A))_(m)(L_(B))_(n), having the structure:

wherein m+n=3; and wherein R³ is selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof.
 14. The compound of claim 13, wherein the compoundis selected from the group consisting of:

wherein R⁴ represents mono, di-substitution, or no substitution; whereinR⁶, R⁸ and R⁹ each independently represent mono, di, tri, ortetra-substitution, or no substitution; wherein Y¹, Y², Y³, Y⁴, Y⁵, Y⁶,Y⁷, and Y⁸ comprise carbon or nitrogen; wherein R⁴, R⁵, R⁶, R⁷, R⁸ andR⁹ are each independently selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof; and wherein any adjacent substitutions in R¹, R²,R³, R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ are optionally linked together to form aring.
 15. The compound of claim 14, wherein the compound is selectedfrom the group consisting of:

16.-24. (canceled)
 25. The compound of claim 14, wherein Y⁵, Y⁶, Y⁷, andY⁸ comprise carbon; and wherein only one of Y¹, Y², Y³, Y⁴ is nitrogen.26.-27. (canceled)
 28. The compound of claim 1, wherein the ligand L_(A)is:

wherein R¹⁰ is selected from the group consisting of of hydrogen,deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy,aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl,aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof.
 29. The compound of claim 28, wherein the ligand L_(A) is:

30.-33. (canceled)
 34. The compound of claim 2, wherein L_(A) isselected from the group consisting of:


35. The compound of claim 2, wherein L_(B) is selected from the groupconsisting of:


36. The compound of claim 13, wherein L_(A) is selected from the groupconsisting of:

wherein L_(B) is selected from the group consisting of:

and wherein the compound is selected from the group consisting ofCompound 1 to Compound 6080, wherein each Compound x has the formulaIr(L_(Ak))(L_(Bj))₂ wherein x=80j+k−80, k is an integer from 1 to 80 andj is an integer from 1 to
 76. 37. A first device comprising a firstorganic light emitting device, the first organic light emitting devicecomprising: an anode; a cathode; and an organic layer, disposed betweenthe anode and the cathode, comprising a compound comprising a ligandL_(A) of Formula I:

wherein each A¹, A², A³, A⁴, A⁵, A⁶, A⁷, and A⁸ is independently carbonor nitrogen; wherein at least one of A¹, A², A³, A⁴, A⁵, A⁶, A⁷, and A⁸is nitrogen; wherein X¹ is selected from the group consisting of O, S,and Se; wherein X² and X³ each independently comprise an atom selectedfrom the group consisting of C, N, O, P, and S; wherein ring A is bondedto ring B through a X²—C bond: wherein ring A is a 5 or 6-memberheterocyclic ring; wherein R¹ and R² each independently represent mono,di, tri, or tetra-substitution, or no substitutions; wherein anyadjacent substitutions in R¹ and R² are optionally linked together toform a ring; wherein R¹ and R² are each independently selected from thegroup consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof; wherein the ligand L_(A)is coordinated to a metal M; wherein M is coordinated to ring A througha metal-carbene bond; and wherein the ligand L_(A) is optionally linkedwith other ligands to comprise a tridentate, tetradentate, pentadentateor hexadentate ligand.
 38. The first device of claim 37, wherein thefirst device is selected from the group consisting of a consumerproduct, an electronic component module, an organic light-emittingdevice, and a lighting panel.
 39. The first device of claim 37, whereinthe organic layer is an emissive layer and the compound is an emissivedopant or a non-emissive dopant.
 40. (canceled)
 41. The first device ofclaim 37, wherein the organic layer further comprises a host, whereinthe host comprises at least one chemical group selected from the groupconsisting of triphenylene, carbazole, dibenzothiophene, dibenzofuran,dibenzoselenophene, azatriphenylene, azacarbazole, aza-dibenzothiophene,aza-dibenzofuran, and aza-dibenzoselenophene. 42.-43. (canceled)
 44. Aformulation comprising a compound comprising a ligand L_(A) of FormulaI:

wherein each A¹, A², A³, A⁴, A⁵, A⁶, A⁷, and A⁸ is independently carbonor nitrogen; wherein at least one of A¹, A², A³, A⁴, A⁵, A⁶, A⁷, and A⁸is nitrogen; wherein X¹ is selected from the group consisting of O, S,and Se; wherein X² and X³ each independently comprise an atom selectedfrom the group consisting of C, N, O, P, and S; wherein ring A is bondedto ring B through a X²—C bond; wherein ring A is a 5- or 5-memberheterocyclic ring; wherein R¹ and R² each independently represent mono,di, tri, or tetra-substitution, or no substitution; wherein any adjacentsubstitutions in R¹ and R² are optionally linked together to form aring; wherein R¹ and R² are each independently selected from the groupconsisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof; wherein the ligand L_(A)is coordinated to a metal M; wherein M is coordinated to ring A througha metal-carbene bond; and wherein the ligand L_(A) is optionally linkedwith other ligands to comprise a tridentate, tetradentate, pentadentateor hexadentate ligand.